The present invention relates to an etching method and apparatus, and more particularly, to a plasma etching method and apparatus for use in the manufacturing of semiconductor devices.
In the manufacturing of semiconductor devices, a functional thin film is first deposited on a semiconductor wafer. Then, unnecessary portions are removed from the thin film using an etching apparatus such as a dry etching apparatus to form a predetermined pattern.
Conventionally, materials that exhibit high reactivities to processing gases have been used for manufacturing semiconductor devices. In an etching step, a semiconductor wafer material is first placed in a processing chamber of a dry etching apparatus, followed by introduction of a processing gas into the processing chamber. The processing gas reacts with the semiconductor wafer material to produce volatile etching products. The etching products are removed from the processing chamber using an exhauster such as a vacuum pump. Therefore, little or no etching products remain in the processing chamber. Also, the wall of the processing chamber is maintained at a high temperature to effectively prevent the etching products from attaching.
In recent years, however, low reactivity materials, which exhibit very low reactivities to processing gases, have been used in the manufacturing of semiconductor devices in response to the trend of miniaturization, higher speed and higher functionality of semiconductor devices. For example, refractory metals having high melting points such as iridium (Ir) and platinum (Pt) are used as materials for electrodes of capacitors in ferroelectric memories (FeRAMs). The high melting point metals hardly combine with other atoms and molecules. Also, PZT (Lead Zirconate Titanate) and SBT (Strontium-Bismuth-Tantalum composite oxide), which are used for ceramic-based ferroelectric materials, have low reactivities.
For etching a low reactivity material, a sputter etching method based on ion collision is used. Etching products produced during sputter etching are non-volatile. The non-volatile etching products are difficult to remove with an exhauster, so they tend to remain in a processing chamber and attach to the wall of the processing chamber. The non-volatile etching products are deposited on the wall in each etching step. The temperature in the processing chamber greatly differs from the etching time to a standby state. Therefore, the deposited etching products are subjected to frequent temperature difference (thermal stress) which causes the etching products to peel off the wall. The etching products, which have peeled off, may drop on a semiconductor wafer. Relatively large pieces prevent the formation of desired patterns in the semiconductor devices.
To prevent such problems, the etching products of low reactivity materials must be removed more frequently than those produced from conventional etching materials. This however increases cleaning costs and reduces the operating time of the etching apparatus. Therefore, a need exists for an etching apparatus that prevents the etching products from attaching to the wall of the processing chamber.
A highly efficient exhauster, which promptly reduces the pressure in the processing chamber, has been used to remove non-volatile etching products from the processing chamber. This exhauster, however, has not been effective. Since the non-volatile etching products have very high melting points, a method has also been proposed for holding the temperature on the wall of the processing chamber relatively high. Unfortunately, this method has also not been effective.
Another method has also been proposed for holding the wall of a processing chamber high while keeping non-volatile deposits from thermal stress. This method does reduce the peeling of non-volatile deposits to some degree. In this method, however, thick non-volatile deposits change the atmosphere in the processing chamber. This makes the etching of semiconductor wafers unstable. Particularly, for etching a material for electrodes of capacitors, metal deposits interfere with high frequency power supplied to the processing chamber, thereby impeding the generation of plasma.
As a method of cleaning a processing chamber, a dry cleaning method introduces a cleaning gas prone to reaction with deposits into the processing chamber, without opening the processing chamber, to subject the deposits to plasma etching. However, the productivity of semiconductor devices is degraded due to interruption of etching when a cleaning sequence is performed.